[jira] [Created] (ARROW-7768) Implement Length and TryClone traits for Cursor> in reader.rs

["David Kegley (Jira)" <ji...@apache.org>]

David Kegley created ARROW-7768:
-----------------------------------

             Summary: Implement Length and TryClone traits for Cursor<Vec<u8>> in reader.rs
                 Key: ARROW-7768
                 URL: https://issues.apache.org/jira/browse/ARROW-7768
             Project: Apache Arrow
          Issue Type: Improvement
          Components: Rust
            Reporter: David Kegley


Currently Length and TryClone are implemented for Cursor<&'a [u8]> in src/file/reader.rs



Attempting to create a cursor from a Vec<u8>


{code:java}
fn test_cursor_and_file_has_the_same_behaviour() {
  let mut buf: Vec<u8> = Vec::new();        
  get_test_file("alltypes_plain.parquet")            
    .read_to_end(&mut buf)            
    .unwrap();        
  let cursor = Cursor::new(buf.as_slice());
...
{code}
 

results in:

 
{code:java}
`buf` does not live long enough

borrowed value does not live long enoughrustc(E0597)reader.rs(681, 34): borrowed value does not live long enoughreader.rs(681, 34): argument requires that `buf` is borrowed for `'static`reader.rs(691, 5): `buf` dropped here while still borrowed
{code}
 

 

Implementing Length and TryClone for Cursor<Vec<u8>> would allow for:


{code:java}
fn test_cursor_and_file_has_the_same_behaviour() {        
  let mut buf: Vec<u8> = Vec::new();        
  get_test_file("alltypes_plain.parquet")            
    .read_to_end(&mut buf)            
    .unwrap();        
  let cursor = Cursor::new(buf);
  let read_from_cursor = SerializedFileReader::new(cursor).unwrap();
...
{code}

Otherwise, buf: Vec<u8> must be declared static in order to initialize a SerializedFileReader from a Cursor.

I'm new to rust so perhaps this is the intended behavior, but if not I'm happy to submit a PR for this

 



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